In a conventional semiconductor module of an array type, plural optical fibers for propagating optical signals are arranged in parallel with each other at a certain lateral pitch, and a semiconductor laser for supplying the optical fibers with the optical signals is used as a light source. The semiconductor laser is composed of plural semiconductor laser elements of the same number as that of the optical fibers. The semiconductor laser elements are arranged at the same lateral pitch as that of the optical fibers, and unified to form a single chip, which is mounted on a substrate.
However, on the aforementioned semiconductor laser, following disadvantages have been pointed out, because this device is fabricated by unifying the plural semiconductor laser elements to form a single chip and mounted on the substrate. First, thermal stress at the time of mounting is high. Second, heat radiation characteristic of the semiconductor element is low, and the effect of thermal interference between channels (the semiconductor laser elements) is noticeable. Third, the yield rate of the unified chip is poor.
When the yield rate of the unified chip is taken into consideration, even in case that the one of the semiconductor laser element is a failure and the remaining ones normally operate, the chip is regarded as a failure also, and the other normal semiconductor laser elements are in vain. The aforementioned uselessness becomes noticeable as the number of the channels increases. Accordingly, it seems to be advantageous to mount the individual semiconductor laser elements in conformity with the lateral pitch of the optical fibers, without using the chip, which is obtained by unifying the plural semiconductor laser elements, in order to avoid the aforementioned uselessness in the normal semiconductor laser elements. However, the lateral pitch of the optical fibers is minute, and it is extremely difficult to mount the semiconductor laser elements on the substrate at the same pitch as that of the optical fibers.